MicroRNA-132 Modulates Cholinergic Signaling and Inflammation in Human Inflammatory Bowel Disease

Abstract

A feedback loop, termed the anti-inflammatory reflex, exists between the immune system and the nervous system. Inflammation triggers an afferent vagal response that is transmitted to the hypothalamus, where it stimulates the efferent vagal nerve to release the neurotransmitter acetylcholine. Acetylcholine activates its nicotinic receptor on macrophages through which it inhibits production of pro-inflammatory cytokines. Multi-leveled evidence suggests a role for the anti-inflammatory reflex in the pathogenesis of inflammatory bowel disease (IBD). Electrical stimulation of the vagus nerve attenuated DSS-induced colitis in rats. Similarly, in vagotomized mice, DSS-induced colitis was more severe compared to control mice and sympathectomy improved experimental colitis. Although, the anti-inflammatory reflex has not been studied in human IBD, enteric nervous system abnormalities in IBD patients, may support its potential role in the pathogenesis of this disease. MicroRNA-132 (miR-132) targets acetylcholinesterase (AChE) and potentiates the cholinergic blockade of inflammatory reactions in cultured cells and experimental mice, but the implications of this interaction to human inflammatory disease remained unexplored. This study aimed to test whether vagal tone (assessed through AChE activity) correlates with inflammation and whether miR-132 is causally involved in anti-inflammatory reactions of patients with IBD and modulates vagal tone and consequently inflammation in IBD patients compared to healthy controls (HC). We prospectively collected clinical data and measured inflammation readouts and the cholinergic status (total capacity for hydrolyzing acetylcholine in one’s circulation), as well as AChE activity in two independent cohorts of IBD patients and HC (Cohort 1: n = 77 IBD, n = 74 HC and cohort 2: n = 33 IBD, n = 16 HC participants). We quantified miR-132 levels systemically in peripheral blood and locally in intestinal tissue biopsies removed at colonoscopy from inflamed and apparently quiescent tissues of tested volunteers. MiR-132 levels are higher in inflamed compared to apparently quiescent intestinal biopsies from IBD patients, while systemic levels were unchanged among groups. Correspondingly, the cholinergic status as well as AChE activity was significantly lower in IBD patients suffering from moderate-severe disease as compared to HC or IBD patients presenting low disease severity. IBD patients (n = 33) presented lower AChE activity compared to HC (n = 16) (289± 128 AU vs 391± 102AU, P = 0.001), and a negative correlation between AChE activity and C-reactive protein (CRP) levels (r = -0.47, P = 0.01). Corroborating these observations in an additional cohort of participants, CRP and AChE activity were negatively correlated in patients with moderate-severe disease (n = 16; r = -0.6, P = 0.04) and positively correlated in HC (n = 74, r = 0.24, P = 0.046). We demonstrated a strong negative correlation between AChE activity and hs-CRP that is disease severity dependent in IBD patients and maybe locally regulated by colonic miR-132, suggesting a new insight to inflammation regulation in IBD. This may signify dual protective role for cholinergic status on inflammation where in acute inflammation cholinergic status enhances the inflammatory process to overcome triggering events such as infections, but in chronic inflammatory states the cholinergic status promotes amelioration of the inflammatory process to restore homeostasis. This may implicate a novel homeostatic mechanism involving a miR-132-mediated change of the cholinergic status in IBD.